Why do gene frequences in a population change and why don't they stay the same?

Gene frequencies in a population do not remain the same
and are always changing. Scientists have classified the causes of this change
into

1. mutation


2. migration


3. drift


4. natural
   selection

Mutations are very rare and changes
in gene frequencies due to this are very slow.

When
organisms of a species that have formed a distinct group interact with organisms of
other groups, they are able to transfer some characteristics that they have and which
are not present in the other group. This is referred to as
migration.

When genes are passed on from parent to
offspring there is a small amount of variation which can be attributed to probability.
These are totally random in nature and are known as genetic
drift.

One of the leading causes of changes in gene
frequency is natural selection. Organisms of a species that have traits which are
favorable for their survival in a particular environment are in a better position to
pass on their genes to the next generation than organisms which do not have these
traits. This slowly alters the gene frequency with the genetic information favorable for
the advancement of the species getting engrained in the genes of all organisms of the
species.